An antenna is an electrical device that sends or receives signals. More specifically, an antenna acts as the port through which radio frequency (RF) energy is radiated to or received from the outside world. A common antenna is an omnidirectional antenna. An omnidirectional antenna radiates in all directions, essentially in a 360 degree pattern. However, such an antenna is an inefficient solution for a problem requiring more directed or focused radiation. A single robust antenna capable of focusing its radiated power on one of several particular areas is desirable partly because of its efficient power allocation and partly because of the direct cost savings in production and potential use in more advanced commercial applications.
A sector antenna provides a common solution to this problem. A sector antenna is an antenna that divides a 360 degree spherical area into smaller segments, such as two 180, three 120, or four 90 degree areas. The sector antenna then generally radiates primarily in a direction of a particular segment to provide a more focused radiation to a particular geographic location. This concentrated radiation in a particular direction increases the directive gain of the antenna, making the antenna more efficient. There are however drawbacks to these standard sector antennas. Each particular sector antenna is designed and constructed to radiate only at a particular degree angle to cover a predetermined area. Once constructed to meet these predetermined specifications, the standard sector antenna cannot be modified. For example, a sector antenna may be constructed to direct its radiation at a 45 degree angle to cover a particular geographic area. A problem arises if the application changes and it becomes necessary to radiate towards a different area, or at a different angle. In such a case, one must design and manufacture several sector antennas for various aperture angles corresponding to different geographic areas. Because each sector antenna is suited only for a particular scenario, it is necessary to change the characteristics of the antenna to respond to a change in the scenario. Thus, one traditionally has been required to swap the antenna with a replacement sector antenna suited for the new scenario, or to electrically modify the existing antenna to address the change in the scenario. A replacement antenna increases the production cost, as two separate antennas must be manufactured, and requires complete replacement of the entire antenna.
In certain instances, a sector antenna may be electrically modifiable, or “smart”. A smart sector antenna may be used in an attempt to meet different parameters or specifications. A switched beam antenna is just such a type of smart antenna. However, a switched beam antenna concurrently produces multiple beams, resulting in a more complex and costly design, and multiple active beams result in losses and inefficiencies. Generally, a two-way antenna to handle the above-described smart sector antenna, built with an electrically modifiable radio frequency (RF) switch has about a 3 to 3.5 dB loss due to the electronic reconfiguration when compared to a standard non-reconfigurable sector antenna. This loss is unacceptable in many sensitive applications. Thus, a smart sector antenna is not a viable option in many instances due to system complexity, cost, and its inherent additional signal losses.
Furthermore, sector antennas are constructed to radiate at a fixed polarization. Polarization of an antenna relates to the orientation of electromagnetic waves at a distance from their source. For example, the electromagnetic waves may be oriented vertically or horizontally. Proper polarization maximizes antenna performance, and generally, the best results are achieved when the polarization of a transmitting antenna matches the polarization of a receiving antenna. The polarization and directivity of such antennas are built into the antenna radiator structure and cannot be changed. Thus, a problem arises when a need exists to radiate a signal over an area with a polarization that does not match the polarization of the sector antenna. In such a case, replacement of the sector antenna and its resulting drawbacks is again the only viable option.